1. Field of the Invention
The present invention relates to a double-face driving silent chain engaging with sprockets within and without the endless silent chain as well as to a double-face driving silent chain power transmission device using the silent chain.
2. Description of Related Art
Recently, it has been proposed to use a silent chain as a timing chain for transmitting rotation of an engine crankshaft to a camshaft and to a shaft of auxiliary unit, such as an oil pump. To that end, Japanese Patent Gazette Nos. 3,182,387 and 3,122,058 have proposed a double-face driving silent chain wherein pluralities of link plates on the right and left ends of the silent chain compose an exterior driving link train with their teeth oriented to the outside of the chain and pluralities of link plates interposed between the exterior driving link plates compose an interior driving link train with their teeth oriented to the inside of the chain.
Japanese Patent Gazette No. 3,182,387, which has been proposed by the present applicant, has proposed a silent chain 1 wherein the exterior driving link train is composed of link plates having the same shape with the link plates of the interior driving link train and are linked by pins on the both right and left sides of the interior driving link train so that their teeth orient to the outside (outer peripheral side).
Japanese Patent Gazette No. 3,122,058 has proposed a silent chain composed of an interior driving link train for which standard link plates are used and an exterior driving link train composed by linking link plates having main engaging teeth within and sub-engaging teeth without the chain with link plates having a flat face within (back) and small sub-engaging teeth orienting to the outside similarly to guide link plates on the both right and left sides of the interior driving link train.
The silent chain 1 in Japanese Patent Gazette No. 3,182,387 is composed of the link plates 3 (31) of the exterior driving link train 2 having the same shape with the link plates 6 of the interior driving link train 5 as shown in FIG. 9A, so that the length thereof to a flat back face 3a is shorter than that of the link plate 6 to a tooth 6a in terms of the distance from a sprocket 9. That is, the length a from a pin 7 to the back face 3a is shorter than the length h from the pin 7 to the edge of the tooth 6a (a<h). It is noted that in FIGS. 9A and 9B, the hatched link plates and whited link plates adjoin each other in rank and are alternately connected by the pins. Additionally, FIGS. 9A and 9B show the interior driving sprocket 9 and a tooth 9a thereof. The distance from the pin is a distance from the center of the pin.
Accordingly, while the inner link plate 31 of the exterior driving link train 2 of the silent chain 1 described above abuts against the side face of the tooth 9a of the sprocket 9 so as to guide and engage the silent chain continuously with the sprocket 9, the length a of the link plate 31 to the back face 3a is short as described above and its function as a guide is insufficient. When the silent chain 1 is used as a timing chain of an engine in particular, the silent chain 1 is apt to engage with the tooth 9a of the sprocket in a twisted manner, as shown in FIG. 9B, due to vibration of the engine itself or pulsatory motion of torque of a camshaft. This twisting causes a back corner portion D of the inner link plate 31 to strike against the side c of the sprocket tooth 9a and, the inner link plates 31 are interposed per pitch (rank), which often causes noise. Furthermore, because the tooth 6a of the interior driving link plate 6 of the silent chain 1 does not fully abut against the tooth 9a of the sprocket in this state, engaging pressure increases due to the partial unbalanced abutment, a crotch plane x and a flank plane y of the link plate shown in FIG. 2 as well as the surface of the sprocket tooth wear quickly, thus shortening their duration of life.
The silent chain of Japanese Patent Gazette No. 3,122,058 requires three kinds of link plates such as outermost plates (guide plates) and inner link plates (node train plates), beside the link plates of the interior driving link train. Accordingly, it is cumbersome to assemble such a silent chain. The strength of the whole silent chain is also weakened because the inner link plate is formed so that main engaging teeth orient to the inside (inner peripheral side) and sub-engaging teeth to the outside (outer peripheral side) and so that the sectional area of the center part thereof is small, thus decreasing its tensile strength, and because such an inner link plate is disposed in a rank (transverse row) on the side having one less link plate among ranks alternately linked by pins. Furthermore, because the link plate of the exterior driving link train is composed of the short sub-engaging teeth, it may not engage fully with the sprocket, thus causing deviation of teeth and early wear of the face of the teeth.